Damaged wiring in centre wing fuel tanks (CWT) of some Boeing 747 Classics, which has been uncovered in the wake of the Trans World Airlines Flight 800 crash in 1996, has led the US National Transportation Safety Board (NTSB) to recommend mandatory inspections.
The US Federal Aviation Administration was also urged to issue a second airworthiness directive (AD) requiring early replacement of Honeywell Series 1-3 terminal blocks on 747 fuel probes because the present ones can chafe the wiring for the fuel quantity indication system (FQIS). Similar investigation is recommended for other Boeing aircraft, including the 757 and 767.
The NTSB recommendations centre on the 747-100/200/300 series, following the TWA 747-100 crash off Long Island, New York, in which a fuel tank exploded, the ignition source for which has still not been determined. Investigators found damaged wiring in the TWA 747 FQIS and in five other 747s. Boeing stopped using Honeywell 1-3 fuel probes in late 1969, but there was no fleet retrofit.
The FAA plans a notice of proposed rulemaking (NPRM) requiring inspection of FQIS wiring inside 747 fuel tanks. Also planned is an AD requiring terminal block replacement.
Late last year, the FAA issued an NPRM to protect the 747 FQIS against transient voltage spikes or short circuits, using suppressors or shielding and separation of FQIS wiring from other wires.
Source: Flight International
